1. Field of the Invention
The present invention generally relates to a transmission and lubrication arrangement for all terrain vehicles. More particularly, the present invention relates to reducing all terrain vehicle engine size through improved lubrication and transmission units.
2. Related Art
All terrain vehicles are often operated in open terrain under difficult running conditions. While such vehicles often may have unrestricted size, it is desirable to decrease the size and weight of the vehicle. For instance, a smaller vehicle allows its operator to maneuver into locations previously unreachable by the larger vehicles. Moreover, decreasing the size and weight of the vehicle increases the power to weight ratio of the vehicle as well as increases the fuel economy of the vehicle.
In the past, in some all terrain vehicles, the selectively engageable two-wheel drive to four-wheel drive transmissions were positioned such that the shifting was done at the differential units, specifically at the front differential unit. Because the differential unit had to have an increased size for such shifting, the weight distribution of the vehicle was shifted toward the front wheels. Additionally, the frame had to be structured to support the increased weight.
In such vehicles, a lubrication system was also disposed within a portion of the crankcase. The system provided moving components within the crankcase with lubricant through passageways and the lubricant would return to an oil pan under the force of gravity. In such systems, the oil pan may encase a portion of the drive shaft. Because of the increased width of the oil pan required to accommodate the drive shaft, the lubricant within the oil pan was capable of sloshing due to the rough terrain over which the all terrain vehicle traveled. The sloshing resulting in widely varying lubricant levels within the lubrication system. Sometimes the level would drop below the level of a lubricant pump pickup positioned within the oil pan. Moreover, the rotation of the portion of the drive shaft positioned within the oil pan sometimes caused an entrainment of air within the oil supply. In both such instances, the lubricant pump would disadvantageously draw air through the system rather than lubricant.
Accordingly, one feature of the present invention involves a shiftable transmission designed to centralize a mass associated with the transmission capable of selective two-wheel drive or four-wheel drive. Another feature of the present invention involves a crankcase design and lubrication system capable of reducing the lateral dimension of the oil pan such that lubricant sloshing does not degrade lubricant system performance.
Therefore, one aspect of the present invention involves an all terrain vehicle comprising an engine, a front wheel and a rear wheel. The engine has a generally laterally extending crankshaft with a crankcase enclosing the crankshaft. A v-belt transmission is coupled to the crankshaft and generally comprises a driven pulley, a drive pulley and a belt extending between the driven pulley and the drive pulley. A generally vertical wall divides the crankcase into an auxiliary chamber and a crank chamber. The v-belt transmission is positioned at least partially within the auxiliary chamber while a lubricant pump is positioned within the crank chamber. The v-belt transmission is generally positioned vertically above, and is connected to, a drive shaft that extends longitudinally within the auxiliary chamber of the crankcase.
Another aspect of the present invention involves an all terrain vehicle comprising a frame, an engine, at least one front wheel and at least one rear wheel attached to the frame. The engine has a generally laterally extending crankshaft with a crankcase enclosing the crankshaft. A generally vertical wall divides the crankcase into an auxiliary chamber and a crank chamber. A gear box is defined within a portion of the auxiliary chamber. A lubricant pump is positioned within the crank chamber while a drive shaft extends longitudinally within the auxiliary chamber of the crankcase. A shaft drive mechanism comprises an input shaft connected to the crankshaft and an output shaft extending from within the crank chamber into the gear box. A first drive shaft is coupled to the output shaft and a second drive shaft is selectively coupleable to the drive shaft. A shiftable coupling mechanism positioned between the second drive shaft and the output shaft and located at least partially within the crankcase. The coupling mechanism is capable of shifting to drive one of the front wheel or the rear wheel or to drive both the front wheel and the rear wheel.